This invention relates to an electronic circuit for producing an audible characteristically unique signal.
More specifically, this invention relates to circuitry which can be driven by a low DC voltage source and designed to activate an alarm when an associated contact is closed. The circuitry may be utilized in a horological device such as a clock or wrist watch as well as many other applications in which a unique tone would be desirable in an alert situation, e.g., doorbell, telephone, etc.
Electromagnetic transducers which include automatic vibrating elements are well known in the art and are commonly activated by a low DC voltage source, such as of 1.5 volts, at the closure of a contact switch. Further, alarm/alert devices of the electrodynamic or ceramic transducer (piezoelectric) type are well known and many are powered by low power circuits utilizing digital integrated circuit technology such as by building the active components using CMOS (complementary metal oxide semi-conductor) technology.
In driving a transducer such as a piezoelectric disk, it is known that increasing the voltage across the transducer increases the forces and strains on the transducer and the performance of the transducer is accordingly improved.
In the past, the frequency or wave form of the signal driving the vibrating transducer was not flexible enough to take into account artistic considerations involving the harmony of the emitted tone from the transducer. Further, the activation of the transducer element typically required transistor switching circuitry and separate discrete components to form an oscillating network.
The foregoing problems have been substantially eliminated by providing in a preferred embodiment of this invention a circuit which efficiently drives a transducer with a voltage much higher than that of the power supply and utilizes in a unique manner the intrinsic capacitance of the associated transducer. Flexibility is provided by the utilization of a multiple stage binary divider to generate many waves of fractional frequency to be modulated in any manner desired by the designer to achieve a multiplicity of tones and harmonies when the alarm/alert transducer is activated, all in a compact reliable manner.